This invention was made with Government support under Government Contract No. 70NANB5H1148 awarded by NIST. The Government has certain rights in this invention.
This invention relates generally to computed tomography (CT) imaging and, more particularly, to scanning an object of interest with a CT scanner.
In at least one CT system configuration, and during a scanning process, an x-ray source projects an x-ray beam towards a detector and the x-ray beam passes through the object being imaged. In known industrial CT systems, for example, the object being imaged is positioned on a manipulator which rotates the object during the scanning process. The beam, after being attenuated by the object, impinges upon the detector. The detector includes an array of generally rectangular detector cells, and the intensity of the attenuated beam radiation received at each detector cell is dependent upon the attenuation of the x-ray beam by the object. Each detector cell, or element, of the array produces a separate electrical signal that is a measurement of the beam intensity at the detector cell location. The attenuation measurements from all the detector cells are acquired separately to produce a transmission profile.
The x-ray beam received at the detector array typically includes two components, namely, a primary signal and a scatter signal. The scatter signal typically reduces resolution and contrast in reconstructed images, which is undesirable. To reduce the impact of scatter signals, a collimator can be placed over the detector. The collimator is configured to substantially prevent scatter beams from impinging upon the detector cells.
While stationary collimators generally are satisfactory for reducing the affects of scatter signals in one-dimensional, or linear, detector arrays, such collimators may not provide optimum results when used in connection with multi-dimensional, or area, detector arrays. Particularly, the pitch of the detector elements in area arrays may be orders of magnitude less than the pitch of the detector elements in linear arrays, and stationary collimators may not be as effective when used in connection with such small pitch detector elements.
To reduce the contribution of the scatter signal received at area detector arrays, a CT system can be configured to directly measure either the scatter signal or the primary signal. The component of the measured signal due to scatter can be determined and then subtracted from the total signal to generate substantially uncorrupted projection data. Directly measuring either the scatter signal or the primary signal, however, is complex and time consuming.
It would be desirable to reduce the contribution of scatter to an image reconstructed from data collected by an area detector in a CT system. It also would be desirable to reduce the contribution of scatter without directly measuring the primary or scatter signal.